Thermal surfacing with self-fluxing nickel based alloys plays an important role in the wear protection of tools in the glass container industry. Bottle machine tools work under very severe conditions, subjected to both wear, corrosion and fast thermal cycling.
Major properties of self-fluxing nickel based alloys are good abrasive resistance and good corrosion resistance at high temperatures. This has led to the extensive use of nickel alloys for surfacing cast iron parts in the glass bottle manufacturing industry. Hardfacing processes with powder welding, Flame spraying, High velocity oxy-fuel (HVOF) spraying and PTA welding use self-fluxing powder in the production of new molds, plungers, baffles, neck rings, plates etc. as well as for repair and maintenance.
Essential elements in a self-fluxing alloy are silicon (Si) and boron (B). These two elements have a very strong influence on the liquidus temperature. The melting temperature for pure nickel (Ni) is 1455° C. The alloy liquidus can be reduced to below 1000° C. by increased concentration of Si and B. The melting temperature range is defined by the solidus and liquidus (FIG. 2a/2b). The low melting points of the self-fluxing alloys is of great advantage, as these can be coated without fusion to the base metal. Alloys normally contain chrome (Cr), iron (Fe) and carbon (C), and at times molybdenum (Mo), tungsten (W) and copper (Cu) are also added. Other metallic oxides, such as Fe and Ni oxides, dissolved with Si and B have the ability to form silicates. This may be important during application of nickel based alloys, as the Si—B slag acts as a welding flux. This protects the fresh metal surface from being oxidized and ensures better wettability for the molten metal.
The microstructure of Ni—Cr—Si—B-alloys is a relatively ductile Ni-rich matrix with various amounts of hard particles. Increasing the amount of alloying elements increases the number of hard particles and consequently the hardness of the alloy. Increased hardness also makes the material more difficult to machine. In soft alloys with low concentrations of Si, B and Cr the predominant hard phase is Ni3B.
It is desirable to produce molds, plungers, baffles, neck rings, and plates with prolonged lifetime, and there is consequently a need to develop new alloys which can achieve this.